How will the selection of allies work? For example in the Early Middle Ages I choose Romano British they have three possible allies to select from. Two of these are Roman which are not available as a main army. Can one of these Roman armies be selected as an ally?

Division D Rob123 (Romano British) defeated uneducated (Jewish 64BC-6AD) 66-45. This battle was constrained by mountains and a large lake so that when the two armies met there was little finesse. It was a stand and die slog until almost the end when the Jewish force ran out of units to throw into th...